The present invention is related generally to evaporating systems for evaporating liquid from chemical samples and, more particularly, to evaporating systems which are capable of rapidly evaporating liquid from chemical samples held in supply plates of varying heights, such as either standard micro-plates or deep well micro-plates.
It is often desirable to transfer a chemical sample from one solvent to another. For example, in liquid chromatography, a sample, perhaps a liquid fraction obtained from one chromatographic procedure, can be more specifically analyzed by use of a different solvent. Further, to reduce spills and the likelihood of cross-contamination and to prevent degradation, due for example to oxidation, samples are often placed within wells and dried by evaporating the solvents in which they are dissolved. It is common to place the well holding the dissolved sample into a heated bath and contact the sample with sufficient inert drying gas to evaporate the unwanted solvent.
Previous evaporation systems have used hot water baths, (heated gas), or mass-to-mass heat conduction to maintain higher sample temperatures during evaporation. These systems were primarily adapted to evaporate samples in individual test tubes and glassware.
Lately, laboratories have been reducing the volumes of expensive solvents used to dissolve samples. Not only are the solvents expensive, but safety and environmental concerns make excessive use of such solvents undesirable. Accordingly, more and more laboratories are switching from test tubes and glassware to micro-plates and deep well micro-plates which have significantly lower volume than test tubes and glassware. Also, such plates are standard in size, stackable, less cumbersome and make handling and storage much easier.
Plates such as these are available in a variety of standard sizes, including the most common ninety-six well plate, available in either shallow (standard) or deep (deep-well) configurations. Although the footprint of both a standard and a deep-well plate are identical for a given number of arrays, plate heights differ substantially. Standard micro-plates are approximately 12 mm high while deep-well plates are approximately 39 mm high. It is also anticipated that wells of various other heights will be introduced as technology develops and needs change.
The process of evaporating solvents from samples can be quite expensive. Drying gas, lab and equipment times, and heating energy are some of the expenses which require consideration and make evaporation efficiency of special concern. In order to evaporate a solvent from a sample most efficiently, it is critical to precisely control the positioning of the sample relative to the drying gas flow, to control the exposure of the sample to the drying gas, and to optimize the warming of the sample by the bath.
Previous evaporation systems have not been well adapted to drying well plates of various heights. As a result, drying gas is positioned to properly contact only one type of plate, or the flow path of the gas is compromised to allow the non-optimized drying of various plates. In U.S. Pat. No. 5,937,536, Kieselbach describes a system intended to dry both standard and deep-well plates by physically accepting either and exposing each to a nitrogen gas flow from a high or a low manifold. In order to accommodate the deep-well plates however, the manifolds must be positioned far aside from or above the plate positions, reducing the efficiency of evaporation from either type of plate by not allowing the gas to be injected directly from the manifold to the sample.
Previous systems have also been only marginally effective at removing the vaporized solvents that tend to gather over the samples as they evaporate. By forming a cloud of solvent vapor immediately above the surface of the dissolved chemical sample, the evaporated solvents reduce the vapor pressure differential at the surface and reduce the rate at which the solvents further evaporate. Effective removal of the vapor is critical to efficient evaporation. Systems such as Kieselbach""s, wherein the flows of inert gas and exhaust gas are remote from the surface of the sample are particularly inefficient at evaporating the solvents and removing the vapor that is formed.
Previous systems have also suffered by lacking an effective method of heating the samples. Mass-to-mass heat conduction has proven inefficient and prone to heating the samples unevenly. Hot water baths leave the plates wet after evaporation. Since plates are stackable and often carried and stored atop one-another, cross-contamination is a problem with samples coming out of a hot water system. Also, multi-well plates which are most commonly used nowadays have a closed upper surface which forms an air trap and does not allow hot water to rise around and envelop the wells, making hot water baths very inefficient at warming such plates. Hot air has proven to be the most effective in drying samples, but the introduction of air can counter the effects of the inert drying gas. In systems where the drying gas is not injected directly into the sample, and the warming air is not isolated from the drying gas, such as Kieselbach, the drying gas would be prone to mixture with the air and could thereby become diluted and contaminate the sample.
Further, previous systems do not allow for the independent evaporation control of multiple plates. Systems such as Kieselbach subject all plates to the same conditions. A deep-well plate holding one type of sample and a standard plate holding another type of sample can certainly be placed into Kieselbach""s chamber, but individual and independent control of the evaporation parameters to each plate is impossible.
A system is therefore desirable, but so far unavailable, which can accept and effectively dry samples in plates of many various heights without compromise, and which can effectively subject the samples to a warming bath of hot air while not diluting or damaging the beneficial effects of the inert drying gas before it contacts the sample.
The object of the present invention, therefore, is to provide a system for evaporating dissolved chemical samples which is adaptable to sample plates of a variety of heights.
It is a further object of the invention to provide such a system, which efficiently exposes samples of all heights to the most effective flow of drying gas.
It is a further object of the invention to provide such a system, which most effectively warms samples of all heights to accelerate evaporation by subjecting them to a bath of warm air.
It is a further object of the invention to provide such a system in which the warm air does not decrease the effectiveness of the drying gas by diluting it before it contacts the sample.
It is a further object of the invention to provide a more effective means for heating the individual wells in a supply plate by a hot air bath.
It is a further object of the invention to provide a more effective means for removing the solvent vapors from above the samples.
It is a further object of the invention to control simultaneous flow of inert gas to multiple plates independently.
It is a further object of the invention to control simultaneous flow and temperature of warming air to multiple plates independently.
The present invention is an apparatus for evaporating solvents from chemical samples, which includes one or more of a series of adapters that each mate to a supply plate of a different height to thereby position the top surface of the plate at a level which is consistent from plate to plate. Inert gas is injected into the upper surface of each sample, and since that upper surface is always at the same level, regardless of the plate height, the relationship of the inert gas injectors and the supply wells is consistent, regardless of the plate height.
Further, the adapters are hollow to allow fan-forced hot air from underneath the plate to bathe each well individually by evenly enveloping the outer wall of each well. This accelerates the evaporation most efficiently while avoiding mixture with and dilution of the inert drying gas that contacts the samples.
Still further, a parallel flow of fan forced air entrains the inert gas/solvent vapor mixture after that mixture evaporates from the sample and carries it from the sample and exhausts it from the apparatus where it can be fed into a fume hood or an exhaust vent. This removal of the vapors immediately above the sample further accelerates the drying process.
The apparatus is contained in a compact and efficient package which allows the user to load and unload two individual supply plates efficiently, and without any disassembly of the apparatus. Further, two plates of differing height can be evaporated simultaneously. It is further provided that the inert gas flow and the hot air flow to each of the two plates may be individually controlled in the event that a different drying process is desired for each plate.